In the past, it was common practice to make the tank for a portable garden sprayer out of steel. Such tanks, while useful for their intended purpose, developed a bad reputation due to catastrophic failures under pressure. All too often, the gardener would overpressurize a tank particularly an older tank which may have been rusted or corroded from use only to have the tank rupture spraying the contents of the tank over the gardener and also propelling the tank through the air toward or away from the gardener as a liquid-propelled rocket.
Today, the steel tanks for portable garden sprayers have been replaced by less expensive molded plastic materials. A reputable manufacturer of a garden sprayer would design the tank to withstand the pressure anticipated in proper useage. When the tank is pressurized by the gardener in a perfectly safe manner, many of these plastic tanks tend to harmlessly develop distortions in the surface which, in view of the bad reputation of the prior metal tanks, tend to alarm the gardener unnecessarily or tend to make the gardener believe he has bought a poor quality or defective tank.